Not Applicable
Not Applicable
1. Field of the Invention
This invention relates to data communication through local loop telephone switching equipment. More particularly, the invention concerns a telephone switch-integrated modem pool and broadband access concentrator providing improved local loop data network access in a manner that reduces data-related congestion in the Public Switched Telephone Network (PSTN).
2. Description of Prior Art
The recent explosion in the growth of the Internet, online services, telecommuting, paging, faxing and other data intensive activities has dramatically increased the usage of modems and caused many congestion issues within the PSTN. Data-related congestion problems include high CCS (Centi-Call Second) access blocking at local switches and trunk congestion in the core transport network. These problems stem from the fact that the PSTN infrastructure was originally designed for ordinary voice calls averaging approximately three minutes in length (e.g., 1.8 CCS/hour). The network was built to handle approximately eight users per circuit at an 8-to-1 user concentration, based on the assumption that if there were eight neighbors on a block, only one of them would normally be on the phone at any given time.
Although adequate for many years, the traditional switch utilization assumptions are no longer viable. Telephony carriers are finding that lengthy data calls from Web surfers are tying up local circuits and network trunk systems and blocking or delaying calls from their mainstay voice customers. Users are now vying for today""s more precious resources to try to get access to circuits. Sometimes a single household may have voice callers, Web surfers and other modem users, as evidenced by the recent growth in the use of second and third lines. As a result of this combined usage, it is not uncommon to see hold times as high as 20 CCS/hour for originating traffic (subscriber side) and 30-36 CCS/hour for terminating traffic (service provider side). With 36 CCS/hour representing 100% line saturation, it will be appreciated that data-related traffic volumes may easily exceed network limits. With the unpredictable patterns caused by data communication usage, irregular hot spots can develop that overload switch capacity and block multiple lines from dial tone.
Consider further that carrying data traffic through the PSTN is very inefficient and thus wasteful of available bandwidth. When a modem call is carried on a voice circuit through the PSTN, it utilizes an entire 64 kbps timeslot even though the data rate is at most about 52 kbps (in the downlink direction). The uplink data rate is even lower. Also, modem connections are idle over 90% of the time (no transmission of information) and therefore average only about 5-8 kbps out of the available 64 kbps capable of being carried on the connection.
To keep up with data traffic demands, one solution is to add more switching and transport resources. However, this would perpetuate the inefficiencies created by dedicating an entire 64 kbps connection for each modem call. Moreover, the cost of such improvements would be high, and revenues may not be sufficient to cover the investment. As a rule, carriers generate little revenue from data network service providers, whose customers connect to their local PSTN switch for hours at a time via modems. With long hold times threatening customer satisfaction, and increased costs coupled with low revenue affecting profitability, an improved low cost solution is needed for handling data traffic in the PSTN.
The foregoing problems are solved and an advance in the art is obtained by a novel telephone switch-integrated modem pool and broadband access concentrator providing improved local loop data network access using the Point to Point Protocol (PPP). Rather than simply cascading PPP packets as TDM (Time Division Multiplexing) traffic through the PSTN, the invention utilizes plural switch-integrated modems, a broadband access concentrator, and a broadband pipe to route the PPP traffic between local loop subscribers (hereinafter xe2x80x9csubscribersxe2x80x9d) and one or more data network service providers (also known as Enhanced Service Providers and referred to hereinafter as ESPs). The switch-integrated modems perform demodulation functions but do not terminate the PPP link with the subscriber. Rather, PPP packets are passed to the broadband access concentrator, which uses layer 2 tunneling to pass the PPP packets over a PPP link formed in the broadband pipe using a network layer tunnel connection. Advantageously, point-to-point connectivity is maintained between subscriber and ESP equipment in order to facilitate continued use of high level subscriber-ESP protocol service negotiation (e.g., PAP/CHAP, NCP and the like). LCP (Link Control Protocol) management and translation between the asynchronous subscriber-to-modem pool link and the synchronous ESP-to-modem pool link are handled transparently by the switch-integrated broadband access concentrator.
In preferred embodiments of the invention, the broadband pipe is an ATM pipe and the modem pool includes a plurality of modems. The broadband access concentrator includes an ATM Adaption Layer (AAL) processing function and an ATM User Network Interface (UNI). The modem pool and the broadband access concentrator may be integrated in a device that includes multiple Modem Application Packs (MAPs), each containing plural modem chips and the AAL processing function, and an ATM Feeder Multiplexer (AFM) (implementing the ATM UNI) mounted in respective slots on a common backplane. The first communication link may include a TDM highway bus incorporated on the common backplane and the second communication link may include an ATM cell bus incorporated on the common backplane.
The AFM is configured to establish either a permanent virtual channel connection or, more preferably, a switched virtual channel connection between the modem pool and the service provider system. The AAL processing function in the MAP performs PPP packet encapsulation/unencapsulation into/from AAL5 CPCS (Common Part Convergence Sub-layer) PDUs (Protocol Data Units), as well as ATM cell segmentation/assembly. The PPP packet-AAL5 CPCS PDU encapsulation/unencapsulation operation is performed according to a convention known as Multiprotocol Encapsulation Over AAL5, a species of which is the Layer 2 Tunneling Protocol (L2TP). The AAL processing function also negotiates LCP options between the modem pool modems and the subscriber equipment on the first communication link, and between the modem pool modems and the ESP system on the second communication link. The AAL processing function also performs LCP conversions between PPP packets carried over the asynchronous and synchronous links.
The foregoing arrangement provides uplink transmission of PPP packets from the subscriber equipment to the ESP system. In particular, uplink packet transmission includes 1) receiving PPP packets from the subscriber equipment at the modem pool, 2) performing demodulation at the modem pool modems, 3) performing LCP termination and conversion of the PPP packets in the AAL processing function, 4) encapsulating the PPP packets into AAL5 CPCS PDUs and segmenting the PDUs into ATM cells in the AAL processing function, 5) delivering the cells from the MAP to the AFM, and 6) receiving the ATM cells at the AFM and placing them on the ATM pipe for delivery to the ESP system over the second communication link.
The foregoing arrangement provides downlink transmission of PPP packets from the ESP system to the subscriber equipment. In particular, downlink packet transmission includes 1) receiving ATM cells carrying PPP packets over the ATM pipe (representing the second communication link) at the AFM, 2) delivering the ATM cells from the AFM to the MAP, 3) assembling the ATM cells into AAL5 CPCS PDUs and unencapsulating the PPP packets therefrom in the AAL processing function, 4) performing LCP termination and conversion of the PPP packets in the AAL processing function, 5) modulating the converted PPP packets at the modem pool modems, and 6) routing the modulated PPP packets for delivery to the subscriber equipment over the first communication link.